10 gal, filtered, heated, divided, one betta on each side..
It's been 60 days since i did a 100% water change of a fully cycled tank - I was moving apartments. I unfortunately let the biological filter dry out over a few hours before re-filling. One of my fish died within 24 hours. I replaced that fish with a new one and for now he appears healthy.
That was two months ago. My specs are below. I have been unable to get ammonia under 1.0 for two months! I do 50% water changes 1x a week.
Ammonia 1.0 pph
The only thing that I can tell you about my water source is we had to have the acid neutralizer filters replaced... It's a new building.